docs: def vector_angle_cos(u, v):
      '''
      vector_angle_cos(u, v) yields the cosine of the angle between the two vectors u and v. If u
      or v (or both) is a (d x n) matrix of n vectors, the result will be a length n vector of the
      cosines.
      '''
      u = np.asarray(u)
      v = np.asarray(v)
      return (u * v).sum(0) / np.sqrt((u ** 2).sum(0) * (v ** 2).sum(0))